sound Card mic input standart

[hakyman]

hi everybody
i'am searching for a standart for sound cards but i cant find smth about it. i read much tittles about it but there is no standart  i could find.
is there a standart for sound cards for Acceptable voltage to mic input??????
or what is the worst sound cards max aceepptable voltage for mic input. i working on it and i have no problem with my sound card(ac97 cmedia) with max +/-1.5 V DC but what about other sound cards ??????
thanx

 

[audioguru2]

Hi Hakyman,
There isn't a standard for powering electret mics from sound cards. Some are wired for a 2-wire electret mic and others are wired for a 3-wire electret mic. Completely different.

The output level of a mic is about 10mV but could be as high as a few hundred mV if you sing loudly up-close or put it in a drum or or other loud musical instrument. Many electret mics and sound cards overload with such a high input.

On my old computer my electret mic worked very well. On my new computer it was dead until I turned-up its mic and master controls but is still not sensitive enough. I guess it is designed for headset mics that are so close they have a high output level. ;D

 

[hakyman]

hi Audioguru
i'm not powering the mic from sound card. i use the sound card as a receiver for PC like the Rf TX circuits connected to the PC. actually its again about the ur electronic stethescope project. i wrote a parallel port and  sound card program to monitorising the sound and added a digital filter for better responce but i got some problems with par.port while real time monitrizsing and matlab have so much advantages with sound card mic input. generally sound cards powering voltage is 5 Volt (for stereo)so i think it will accept the 5V but i'm not sure about the current. i tryied the circuit at different 5 PC and had no problem it acts well but i would like to learn standart if it exist i dont think the output of sstethescope project damage any sound card but i'm not sure again ..
thanxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx(and i will add ur name to my thesis "thanks to" part

 

[audioguru2]

Hi Hakyman,
With the stethoscope-2 project powered by 9V batteries, it max output voltage is about +4V to -4V which might be enough to damage the mic input of a sound card. The project's LM386 probably can produce enough current to blow any protection diodes on the sound card.

 

[hakyman]

hi Audioguru
Here is my measurements(all values r max, means i hit the stethoscope head as strong as i could do ;D )

output of steth. circuit;
ACV =1.5V (with no load)
DCV =+/-1.5V(with no load)
ACA =12mA (with no load)
resistance in ohm of PC sound car dmic input=unreadble(over 20Mohm)

when the circuit connected to PC sound card mic input ,current flows to PC;
ACA=0,950 mA

additional info = sound card adds a 0.02mv Ac componenet onto real signal
i use 9V alkaline batteries
and i limt the circuit output voltage with limiter dioades and i set the volume as low as possible cause my main purpose is monitoring the heart and respitory sounds so i did some differences on filter block.
i dont fright from the output voltage but i'm not sure about the current but 0.950mA cant damage any kind of sound card i guess but i want to be sure
and what do  u think. is there any value have no-sense or unexpected???
specially is  0.950mA too low for 1.5V in AC ?
thanxxxxxx

 

[audioguru2]

Hi Hakyman,
The output level of the stethoscope-2 project is much too high to feed a dynamic mic input on a sound card. I suggest you connect it to a line input. If a line input isn't available you can make an attenuator with two resistors and you don't need the LM386 stage nor the volume control.

If you connected diodes across the project's output as a voltage limiter without adding a current-limiting resistor in series, you risk blowing-up the LM386 and/or the diodes.

Please post a schematic with the changes you made to the filter so we can learn what works best for you. ;D

 

[hakyman]

hi Audioguru
i did not do special cahnges on filter block still sallen n key type but i just set the cut-of to 1500Hz coz i said before i work on both heart and respitory sounds and respitory sounds range is 70-1200 hz. i added a digital filter at 8th degree to choose the heart sounds. i know the analog filter seems useles but teachers said there should be an analog type filter so i added
very very best regards